1. Field of the Invention
The present invention relates to hybrid splitters and more particularly to microwave 90 degree splitters.
2. Description of the Related Art
Conventional ninety degree couplers are typically large, having a footprint substantially larger than two inches by two inches.
A conventional 90 degree splitter is shown in FIG. 1. It consists of two transformers T1 and T2 and four capacitors C1, C2, C3 and C4. Typically, the transformer is made by winding twisted wires onto a one hole toroid core. Transformer T1 has wires 11 and 12. Transformer T2 has wires 13 and 14. The connection between two transformers is usually made by soldering the wires from the two transformers together with solder joints SJ1 and SJ2 and then to a grounded capacitor C3, C4 or welding the wires to a common metal pad which has a capacitor connected to a ground G.
Various examples of power splitters are known in the art. U.S. Pat. Nos. 4,789,845, 4,173,742, 4,182,996 and 5,430,418 show power splitters.
As the frequency of operation increases, the values of the capacitors goes down and it becomes difficult to realize them as lumped elements. In general C3 and C4 are smaller than C1 and C2.
It is an object of the present invention to provide a ninety degree splitter that incorporates no capacitors.
It is an object of the present invention to provide a wire wound, wide band ninety degree splitter that is functional above one gigahertz.
The present invention is a ninety degree splitter which covers a wide frequency range of 1500 to 2500 MHz in a small footprint of only 0.2 inches by 0.2 inches. This device does not use any capacitors which greatly simplifies the construction and lowers the cost in comparison to conventional splitters.
The capacitors are eliminated by substituting inter-winding capacitance in the transformers used in the splitter. This eliminates the capacitors, and reduces related process such as extra soldering and welding. The result is a lower cost device with high frequency performance exceeding that obtained with conventional devices utilizing lumped capacitors.
The present invention provides a power splitter that includes a transformer with a core. A first winding (21), a second winding (23), a third winding (22) and a fourth winding (24) are wound on the core. The first and second windings are coupled to the third and fourth windings, such that the inter-winding capacitance between the windings form a third and fourth capacitance in FIG. 1. C3 and C4 are eliminated in lower frequency application.
A further embodiment of the present invention provides a power splitter that includes a transformer with a core. A first winding (31), a second winding (32) and a third winding (33) are wound on the core. The first winding is coupled to the second winding, such that the inter-winding capacitance between the first and second winding forms a first and a second capacitance. The inter-winding capacitance between the first, the second and third winding forms a third and a fourth capacitance in FIG. 1. All four capacitors are eliminated in high frequency applications.